Drive systems for instance for slats and landing flaps on aircraft wings frequently consist of a central drive unit, which is arranged for instance in the fuselage of the aircraft. Via a branching transmission, the central drive unit is connected with transmission shafts in the half wings, which in turn transmit the torque to the flaps via branch transmissions. Downstream of the branch transmissions, actuators and guide transmissions are provided, which move the aerodynamically acting flaps.
Considering the torque level per half wing from outside, i.e. from the wing tip inwards to the wing root, the torque level in the transmission shafts is increased at each load station by the torque branched off there. Thus, at each root-side shaft end, half the operating torque of the drive unit acts, which drive unit usually supplies both half wings with the required torque.
In general, the central drive unit is designed for the maximum occurring operating torque at nominal speed, and after reaching and exceeding the nominal output point, a torque excess except for the blocking torque (stalling torque) becomes effective with decreasing speed. Hence a conventionally designed drive unit has about three times the torque potential than is required for moving a half wing.
Faults occurring in the half wings, which should rather be detected immediately, include the so-called jamming case (jam), i.e. the jamming of a component of the power train or of the flap itself, and the shaft breakage, which leads to the fact that flaps behind the breakage point no longer can be positioned correctly, which can lead to an asymmetric fault.
Without use of a torque limiter, the full stalling torque of the drive unit develops in a jamming case in the series of the power-transmitting components between the central drive unit and the jamming point, which leads to the fact that the entire stalling torque or the actuating force resulting from the stalling torque acts at the jamming point itself, which can lead to a damage of the components to which the torque is applied. Therefore, it is known from the prior art to use torque limiters, by means of which the high component loads can be prevented. By means of the torque limiters, the downstream components of the branch transmission, of the guide transmission and of the structural components are protected against these extreme loads.
These station torque limiters have the effect that they dissipate the torque of the drive unit into the wing structure. The response value of these so-called station torque limiters generally is about 130% of the maximum admissible operating torque of the station.
For lowering the torque level, it is furthermore known from the prior art to incorporate so-called branch torque limiters or also half-system torque limiters in the transmissions behind the branching point, but close to the root, which subsequently are also referred to as half-wing torque limiters. The same are actuated by the station torque limiters. Their response value generally is about 130% of the maximum accumulated operating torque of the half wing.
Aircraft high-lift systems with overload protection are known from the prior art.
DE 103 53 672 A1 describes a system, in which a jamming case is detected by comparing the conditions in the left and right wings. The instantaneous conditions of position, speed, acceleration or output power of drive units are indicated as characteristics to be observed. If a jamming case is detected in this way, the drive unit is deactivated, so that a further torque increase in the transmission system is limited.
From DE 10 2004 055 740 A1, an aircraft high-lift system with overload protection is known. What is provided is the use of a signal generated by means of an electromechanical switching device, which indicates that the threshold value of the operating torque is exceeded in the transmission of the half wing close to the root. If a jamming case in the power train of a half wing is detected in this way, the drive unit is deactivated. Said threshold value lies above the maximum operating torque of the half wing.
DE 103 08 301 likewise describes an aircraft high-lift system with overload protection. In this system, the drive unit is deactivated between the actuator and the guide transmission after a threshold value of the continuously measured actuating force is exceeded.
EP 1 321 359 B1 discloses the constructive features of a differential torque limiter.
As explained above, a further case of fault consists in the occurrence of a shaft breakage (disconnect). A shaft breakage leads to a so-called asymmetric fault, which is problematic in particular because the unsymmetric variation of the uplift and resistance forces on the wings cannot be compensated with the primary flight control surfaces (ailerons). Asymmetry can result from an interruption (disconnect) at an arbitrary point in the transmission system, whereby the flaps or landing flaps no longer can be positioned in a controlled way behind the breakage point.
For detecting the shaft breakage, it is provided in the prior art that the positions of the shaft systems in the left and right wings are measured and compared continuously. When a threshold value of the position difference is exceeded, an interruption (disconnect) is assumed in the power train, and the system is shut down.
FIG. 5 shows an aircraft high-lift system with overload protection known from the prior art.
The drive power of the central drive unit 1 is delivered via the central shaft 2 to the branching transmission 3. In the branching transmission 3, the drive power is distributed into the transmissions 5 of the left and right half wings. For reasons of simplicity, only the components of the right half wing are provided with reference numerals in FIG. 5. The left half wing has a mirror-symmetrically identical construction.
In the jamming case, the half-system torque limiter 4 protects the succeeding elements of the half wing against inadmissibly high loads. Behind the same, the branching transmissions 6 are provided, which take the power necessary for moving the actuators 8 from the transmission line 5. The actuators 8 convert the rotation of the branch transmissions 6 into translatory actuating movements. By means of the guide transmissions 9, the actuating force is transmitted to the respective landing flap 10. Furthermore, they determine the kinematic course of the actuating process.
As can furthermore be taken from FIG. 5, station torque limiters 7 are provided at the outlet of the branch transmissions 6, which protect the components of the station against inadmissibly high loads.
If jamming occurs for instance in the guide transmission 9 of the outer right-hand station, the load in the associated actuator 8 will rise, until the station torque limiter 7 of this station responds and dissipates the driving torques into the structure. Since the drive unit 1 continues to operate, however, the torque in the transmission line 5 continues to rise, until the half-wing torque limiter 4 responds and dissipates the driving torque into the structure.
In this condition, the system is blocked, and in the transmission line 5 between drive unit 1 and half-wing torque limiter 4, the stalling torque, i.e. the maximum possible operating torque is constrained. Between half-wing torque limiter 4 and station torque limiter 7, a torque of about 130% of the maximum half-wing operating torque is constrained, and in the line between station torque limiter 7 and the jamming point about 130% of the maximum station torque and/or of the actuating force resulting therefrom.
Such system operates with both uncontrolled and controlled drive units.
As explained above and shown in FIG. 5, a system topology in accordance with the prior art thus includes a multitude of complex mechanical devices, which increase the system price and the weight, and at the same time impair the system availability also because of the increased complexity, for protecting components against excessive torques/actuating forces.